Welding apparatus



.z azs wa July 20, 1943. M. Q. KUHN WELDING APPARATUS Original Filed June 20, 1940 INVENTOR MAX 0. KUHN J T OFZNEYS Patented July 20, .1943

WELDING APPARATUS Max 0. Kuhn,

Ohio, a corporation Original application June 20, 1940, Serial Cuyahoga Falls, Ohio, assignor to The Firestone Tire &

Rubber Company, Akron, 1 Ohio Fivided and this application April 22, 1942, Serial No. 440,079

4 Claims.

This invention relates to welding apparatus, and more specifically it relates to improved mechanism for electric butt-welding by the Thomson process. The present application is a division of application 341,484, entitled Welding method and apparatus, filed June 20, 1940.

The invention is of primary utility in the manufacture of rims for resilient tires, and will be described with particular reference thereto, it being understood that the invention is capable of wider application and is not thereby limited to the specific illustrated embodiment.

In the manufacture of tire rims, such as the metal tire rims for pneumatic tire casing, the strip of metal is worked by pressing, hot rolling, cold rolling, or by any combination of said operations, substantially to its ultimate transverse shape and profile. Thereafter the strip is bent to circular form, and its ends butt-jointed or spliced by electric welding. Usually the welded annular rim is made to smaller diameter than its ultimate diameter, and requires subsequently to be circumferentially stretched to enlarge it to desired size. During the said stretching operation considerable diiiiculty has been encountered clue to breaking of the weld, and considerable loss has been incurred due to the required scrapping of broken rims. The breaking or" the weld has been particularly prevalent with rims made of a certain g ade of steel, but since this steel is in other particulars the most desirable for the manufacture of tirerims, the solution of the problem was sought in the improving of the tensile strength of the weld.

Accordingly, the chief objects of the invention are to provide improved apparatus for forming an electrically welded connection of superior tensile strength. Other objects include the production of superior rims; the saving of time and labor in the manufacture of said rims; and to effect other savings by obviating losses arising from defective welding. Other objects will be manifest as the description proceeds.

Of the accompanying drawing:

Figure 1 is a fragmentary front elevation of welding apparatus embodying the invention, and the work therein;

Figure 2 is a side elevation, on a larger scale, of one of the lower welding jaws, and the work, shown in section, operatively associated therewith; and

Figure 3 is a section on the line 3-3 of Figure 2.

Briefly, the improved apparatus is adapted to effect the heating of each of the rim-ends to be welded to differential temperatures throughout its area before bringing said ends forcibly together to form the weld. More specifically, in the case of butt-welding the ends of metal strips, such as tire rims the ends of the weld, that is. at the margins of the strip, are heated to a higher temperature than the temperature intermediate thereto. Thus while the ends of the weld may be heated to white heat, the intermediate region may be cherr red in color, The differential temperatures in the rim ends. to be welded are concurrently produced by preventing the direct passage of electric current through the WOlk in a local region of that portion of the work that is to be welded, the magnetic field set up by the welding current undergoing a de crease in density through said local region of the work.

Referring now to Figure l of the drawing, there is shown a portion of a conventional electrical apparatus comprising a pair of lower supportil'lg members or heads l0, ID that are shown in spaced apart relation but are movable toward each other, mounting blocks H, I I that are positioned atop of the respective members l0, and lower jaws or electrodes, designated as a whole by the numerals l2, l2, that are mounted upon the top of the respective blocks ll. Upper jaws or,electrodes l3, I3 of the apparatus are carried by the free ends of respective arms M, the latter being movable angularly to move the upper jaws toward or away from the lower jaws l2. The arms l4 also are movable toward each other concurrently with similar movement of the lower supporting heads It]. When the arms M are lowered the upper jaws I 3 are in opposition to the lower jaw l2 to the end that the respective ends of a split metal ring, such as'a tire rim l5 may be clamped between said jaws as shown. The work engaging faces of the laws l2, 13 are shaped complemental to the rim-surface that they engage so that there is good electrical conductivity therebetween. Suitable electrical conductors (not shown) are provided for supplying electric current of low voltage and high amperage to each of the upper and lower jaws or electrodes in the usual manner.

The upper jaws l3 are of standard construction and usually are composed of steel. The lower jaws l2 are composed of copper, or other suitable metal, and differ from prior constructions in that a local region of the work engaging surface of each is so insulated that no electrical current passes directly therefrom to the work. For thus insulating each jaw l2 from the work,

set portion of the weld is r or other suitable means,

a. layer of mica insulation ll is provided, which layer is mounted in a recess it in the top face of the jaw and overlain with a wear-plate E9 of stainless steel, said members being maintained in assembled relation by screws 2|] that extend through the jaw from the bottom thereof, and are suitably insulated therefrom. The arrangement is such that the wear-plate is fully insulated from the jaw 12, the upper face of the p ate being flush with the adjacent work-engagirtg surfaces of the jaw. The wear-plate and insulation are located intermediate the ends of the work-engaging portionof the jaw, but transversely they extend completely across the jaw, or slightly beyond though mica and stainless steel are used for the insulation and wear-plate respectively, these materials are not essential to the operation of the machine, and other insulating material and superior wearing metal may be provided if found expedient. Experience has shown however, that superior results are obtained when the insulated region of the jaw is as thin as possible, which phenomenon is believed to be due to the fact that the magnetic field set up by the electric current is thereby interrupted to a lesser degree.

Mechanically the apparatus is operated in the same manner as conventional welders of this type. With the pairs of jaws l2, l2 in laterally spaced position and the upper jaws 13 in elevated position, a split rim l is mounted in the g apparatus with its ends resting upon the respeci2 and projecting slightly befaces of the latter. The upper jaws !3 are then lowered so as to confine the rim-ends between themselves and the lower jaws I2 as shown in Figure 1, after which the electric current is passed through the jaws and confined rim-ends therebetween to effect the fusing of the latter. Finally the pairs of jaws are moved toward each other to effect the butt-welding of the heated projecting end portions of the rim. There after the flash or upremoved by grinding after which the rim is ready to be distended to ultimate diameter, as previously has been explained.

Annular articles welded according to the invention may be distended to the desired extent without rupture of the weld. It is believed that this result is due to the fact that heat generated during the fusing of the ends of the article spreads over a larger area of the said ends, thus resulting in a larger annealed area around the weld of the finished article. Evidence of this fact is visible in the finished article wherein the annealed region of the weld is of slightlyg different color than the non-annealed region, is wider at each end of the weld than at the intermediate region thereof, and also that the narrowest annealed region isat least as Wide as the annealed portion of rims welded by conventional methods and apparatus.

The apparatus of the invention is relatively inexpensive to install, and the operation of the tive lower jaws yond the confronting as shown in Figure 3. Al-

apparatus involves no departure from prior practice. The invention provides a superior weld, which is especially desired in the manufacture of tire rims, and achieves the other advantages set out in the foregoing statement of objects.

Modification may be resorted to without departing from the spirit of the invention or the scope thereof as defined by the appended claims, which are not limited to the specific construction shown.

What is claimed is:

1. Electric tire rim butt-welding apparatus comprising pairs of upper and lower electrodes adapted to grip work-units to be joined by welding, and means impeding the direct passage of electric current from the electrodes through the work units in local regions of the latter with which the electrodes are in contact, said means comprising recesses formed in the top faces of the said lower electrodes and extending a substantial distance across the work-gripping surface thereof, insulating material within said recesses, wear-plates overlying said recesses and being retained in position by supports extending through said insulated material, said wearplates being insulated from said lower electrodes and being adapted to cooperate with them in gripping the work.

2. Electric tire rim butt-welding apparatus comprising pairs of electrodes adapted to grip work-units to be united by welding, and insulation locally disposed between one electrode of each pair and the work-units for impeding the direct passage of electric current therebetween, a stainless steel wear-plate overlying said insulation and being maintained in assembled relation by means of screws, said wear-plate being insulated and spaced apart from the assembly.

, 3. Electric butt-welding apparatus comprising pairs of upper and lower electrodes adapted to grip work-units to be joined by welding, and means impeding the direct passage of electric current from the electrodes through the workunits in local regions of the latter with which the electrodes are in contact, said means comprising recesses formed in the top faces of the said lower electrodes and extending a substantial distance across the work-gripping surface thereof, insulating material within said recess, wear-plates overlying said recesses, wear-plate supporting means, said wear-plates being insulated from said lower electrodes and being adapted to cooperate with them in gripping the work.

4. Electric butt-welding apparatus comprising pairs of electrodes adapted to grip work-units to be united by welding, and insulation locally disposed between one electrode of each pair and the Work-units for impeding the direct passage of electric current therebetween, a rigid metallic wear-plate having high heat resistance characteristics overlying said insulation, wear-plate supporting means, said wear-plate being insulated and spaced apart from the assembly.

MAX 0. KUHN. 

